About the Project
Sea ice is a key component of Earth’s climate system, regulating the exchanges of heat and freshwater in the polar regions, and influencing global ocean circulation. Typically covering an area larger than South America in austral winter and shrinking dramatically in summer, Southern Ocean sea ice is one of the most dynamic surfaces on Earth (Shepherd et al., 2018). Highly sensitive to changes in both the atmosphere and ocean, it is also one of our planet’s main indicators of climate change.
The launch of the European Space Agency (ESA) CryoSat-2 satellite in 2010 began a new era of high resolution, Synthetic Aperture Radar (SAR) altimetry, a method for measuring surface elevation via transmission and receipt of a radar pulse. CryoSat-2 has transformed our ability to monitor sea ice thickness in the Arctic, and to track its response to changes in climate [Tilling et al., 2015, 2016]. Despite these advances, we still know little about Antarctic sea ice because heavy snowfall in the southern hemisphere complicates our ability to measure its thickness from space. But in 2018, NASA launched ICESat-2, a laser altimeter which provides an exciting opportunity to measure Antarctic sea ice thickness from space. Sea ice thicknesses is calculated from measurements of its freeboard - the portion protruding above the ocean surface – and although the CryoSat-2 radar signal passes through the snow layer, the ICESat-2 laser does not, and so the measurements can be combined to determine the snow and ice thickness at the same time.
The aim of this PhD is therefore to produce the first continental-scale measurements of Antarctic sea ice thickness, and to explore this dataset to provide the first understanding of spatial and temporal trends which may impact on the region’s climate, natural habitat, and maritime activity. While sea ice coverage of the Arctic Ocean has been on a downward trend for decades, Antarctic sea ice extent was, until recently, growing. The last few years have seen dramatic losses in sea ice coverage of the Southern Ocean, shrinking to a 40-year minimum in 2017 and 2018. The reasons for the observed trends in extent remain unclear, with understanding currently hampered by a lack of Antarctic sea ice thickness and volume measurements. This is therefore a critical time to develop these datasets and help illuminate the drivers of recent change.
Antarctic sea ice thickness will be determined from a combination of CryoSat-2 and ICESat-2 satellite altimetry, a model of dynamic snow loading, and a physical model of the sea ice buoyancy and radar scattering informed by ship-based measurements. There may also be opportunities to participate in polar field campaigns, which play an essential role in calibrating and validating satellite observations.
As a PhD candidate, you will have the opportunity to (1) work with state-of-the-art satellite data, (2) develop expertise in the most recent instrument and processing techniques, and (3) address globally-significant questions relating to climate science.
This PhD is based within the Centre for Polar Observation and Modelling (CPOM), in partnership with the British Antarctic Survey (BAS) and the European Space Agency (ESA). CPOM provides the UK with core strategic expertise in the exploitation of satellite measurements to study the Earth’s cryosphere, using state-of-the-art Earth observation techniques and numerical models to study and predict changes in the polar ice sheets and sea ice cover. CPOM also develops and maintains near real time measurements of Arctic sea ice thickness in partnership with ESA (http://www.cpom.ucl.ac.uk/csopr/seaice.html).
The project will be supervised by Professor Andy Shepherd and Dr Isobel Lawrence at Leeds, with input from ESA and Dr Paul Holland at BAS. Andy is the Principal Scientific Advisor for ESA’s CryoSat-2 mission and an expert in polar climate processes, Isobel is a specialist in radar altimetry, and Paul is an expert in Antarctic sea ice and its recent changes.
The project would suit a numerate candidate with a degree in a discipline such as Physics, Mathematics, Earth Sciences, Computer Sciences or Physical Geography.
Increased Arctic sea ice volume after anomalously low melting in 2013. Tilling, R.L., Ridout, A., Shepherd, A., Wingham, D.J. (2015), Nature Geoscience doi:10.1038/ngeo2489
Holland, P. R. , Bruneau, N. , Enright, C. , Losch, M. , Kurtz, N. T. and Kwok, R. (2014): Modeled Trends in Antarctic Sea Ice Thickness , Journal of Climate, 27 (10), pp. 3784-3801 . doi: 10.1175/JCLI-D-13-00301.1
Shepherd, A., Fricker, H.A. & Farrell, S.L. Trends and connections across the Antarctic cryosphere. Nature 558, 223–232 (2018). https://doi.org/10.1038/s41586-018-0171-6
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